1. Field of the Invention
The present invention relates to a color image forming apparatus, and more particularly to a color image forming apparatus capable of forming a color image in consideration of the reproducible color range.
2. Related Background Art
For improving the color reproducibility, the conventional color image forming apparatus is so designed to effect faithful color reproduction if the color space of the original image is within the color reproduction range of said apparatus, but, if the color space of the original image exceeds the color reproduction range of said apparatus, to convert any color outside said range into a substantially similarly appearing color within said color reproduction range, thereby attaining optimum color reproduction for all the color originals.
In case the color reproduction can be conducted faithfully within the color reproduction range of the color image forming apparatus, the reproduced color image may be recopied as an original, and there is attained an improvement in the color reproducibility in an image obtained by reproducing the thus recopied image.
FIG. 4 is a flow chart showing the sequence of forming a color image by an electrophotographic process.
When a copy start switch is turned on in the color image forming apparatus, a step S41 scans a color original placed on an original table, and the color original image is converted into R, G and B signals by a CCD having color filters on the optical path thereof. Then a step S42 effects color space discrimination based on said R, G and B signals, namely whether the color original is included in the color reproduction range of the color image forming apparatus or contains a color outside said color reproduction range.
The individual parameters have to be varied according to the characteristics of color separation filters, the spectral characteristics of the CCD, the color forming materials and the recording material, and the dot forming method. If the following relations (1) and (2) stand in all the R, G and B signals obtained by scanning, the color space of the color original is included within the color reproduction range of the color image forming apparatus: EQU max(R, G, B)&gt;Th (1)
wherein Th is a threshold value determined from the maximum density of the color image forming apparatus; ##EQU1##
The image processing conditions, for example the coefficients to be used in the density-tendition transformation and the matrix parameters to be used in the masking are prepared in advance and are selected according to the result of said discrimination.
Then a step S44 effects the original scanning for a first color and the image processing with the preset image processing conditions. Then a step S45 forms a latent image of the first color, then a step S46 develops said latent image with a coloring material of the corresponding color, and a step S47 transfers thus developed image onto a recording material.
Then there is discriminated whether the latent image formation, image development and image transfer have been completed for all the colors, and, if not, there are executed the original image scanning, latent image formation and image development for a second color in the same manner as for the first color. Subsequently the obtained image is multiple transferred in registration with the image of the first color, and is fixed. Thereafter the steps S44 to S48 are repeated for all the colors, and, when the latent image formation, image development and image transfer are completed for all the colors, the sequence proceeds to a step S49 to effect image fixation. Thus there is obtained a full-color image with optimum color reproduction.
In such conventional process, however, the first copy time from the start of image formation to the printout of the reproduced full-color image requires about 30 seconds and cannot be reduced, because there is conducted an original scanning for discriminating the color of the original.